Spacecraft such as rockets, satellites, shuttles, transfer vehicles, orbital stations, and other bodies flying in space are typically outfitted with suitable containers or fuel tanks for storing liquid fuels that are used to power the engines, including engines or thrusters for the position regulation in space, as well as engines or thrusters for carrying out apogee maneuvers. In order to drive or propel the liquid fuel out of the fuel tank, the fuel tank is typically also charged with a pressurized driving gas, which pressurizes the liquid fuel and drives it out of the tank to the combustion chamber or reaction chamber of an engine of the spacecraft in which the fuel will be consumed. Inert gases such as helium (He) or nitrogen (N2) are typically used as the pressurized driving gas, for which purpose they are introduced under pressure into the fuel tank and thereby press the fuel into the pipeline system leading from the respective tank to the respective connected rocket engine. In that regard it is important to achieve a complete, reliable and sure separation between the driving gas used as a conveying medium and the liquid fuel being supplied into the engine, because the liquid fuel must absolutely and surely be free of foreign gas inclusions when it is supplied to the engine, in order to avoid combustion problems during ignition and burning of the fuel in the engine.
In the standard conventional fuel systems of spacecraft, the separation of the driving gas from the liquid fuel is achieved either in the fuel tank itself or in a separate bubble trap or gas separation device connected downstream from the fuel tank. In either case, the fuel exiting from the tank outlet or the bubble trap outlet is provided free of gas bubbles or inclusions. In that regard, the positioning of the fuel tanks in the spacecraft has an important influence on the layout or design of the tank. Therefore, it is usually ensured that the tank outlet is positioned at the lowest point of the tank in the direction of the main effective acceleration, so that a bubble-free filling of the tanks on the ground on earth and a complete emptying of the tanks in orbit is possible. In some cases, however, it is desired to arrange or install the fuel tank with its outlet oriented contrary to the main acceleration direction, for example in a lander unit or module that is to land on the moon, or for a fuel tank that is to be transported to the launch area in a horizontal orientation. In these cases, a bubble-free supply of liquid fuel cannot be ensured under some circumstances, because gas can collect in the fuel lines. In those cases it is generally necessary to suitably adapt the fuel tank or to use a specially designed bubble trap connected downstream from the fuel tank.
The quantity of driving gas that can accumulate in the fuel line system from the supplied fuel during a specified space flight mission, is generally known or can be determined. Thus, the quantity or volume of gas that must be reliably separated from the supplied fuel during a given space flight mission is known or can be determined. Furthermore, except for the gas quantities or inclusions that are already located in the fuel line system, the fuel tanks are still able to provide bubble-free liquid fuel even after a gas breakthrough. In that regard, the gas quantity that is to be separated from the liquid fuel in the fuel line system is strongly dependent on the fuel line system volume and is normally small in comparison to the volume of the fuel tank.
Bubble traps or gas separator devices have already become known in the prior art, in various different embodiments, and both for use on the ground on earth as well as in applications in space flight conditions. Several US patent application publications such as US 2001/0,042,441, US 2007/0,239,098, and US 2008/0,171,962, as well as US patents such as U.S. Pat. Nos. 4,102,655 and 6,478,962 disclose example arrangements that serve to filter gas bubbles out of a circulating flow of human blood. In such an application, the separated gas bubbles do not need to be accumulated and stored over a longer period of time. Therefore, the bubble trap concepts disclosed in such patent documents relating to the separation of gas bubbles from blood are fundamentally different from, and not applicable to, the requirements of bubble trap applications in space flight technology. More particularly, the bubble traps or gas separator devices known from these prior patent publications are not designed and are not useable for separating gas from liquid fuel in a spacecraft for space flight.
Furthermore, U.S. Pat. Nos. 5,334,239 and 6,432,178 disclose gas separator devices that are also suitable for use in space flight technology. For example, U.S. Pat. No. 5,334,239 discloses a gas separator or bubble trap that achieves a separation of a gaseous phase from a liquid phase by causing a rotation of the liquid. Namely, the inertia of the liquid is used in a cyclonic separation technique in order to separate the gas from the liquid. It is a disadvantage of such a technique and such a gas separator device, that a separation of the gas from the liquid by means of the inertia of the liquid requires a comparatively large volume flow of liquid. However, especially for the position regulation of a spacecraft, sometimes only very small volume flows of the liquid fuel are needed for operation of the spacecraft engine over very short operating times. Such a low volume flow during such short times is not adequate to achieve a reliable gas separation based on the inertia of the liquid in a cyclonic separation technique. Therefore, the gas separator device known from U.S. Pat. No. 5,334,239 is not suitable in such cases in which only a small volume flow of liquid fuel must be supplied to an engine during short operating times.
The gas separator device disclosed in U.S. Pat. No. 6,432,178 includes a screen arranged orthogonally to the flow direction of the gas-liquid mixture. The gas bubbles are supposed to collect on this screen. However, it is disadvantageous in this known arrangement, that the portion of the screen surface that is already covered with one or more gas bubbles becomes blocked by the gas bubble(s) and thus reduces the remaining surface area that is available for the liquid to flow through the screen. This results in local pressure losses or pressure drops across the screen. This can be problematic especially in that the screen surface area that is covered with the gas bubble(s) must be taken into account when determining the pressure drop or loss through the gas separator device, during the design of the device. As a result, very large screen surface areas can be required for the device. Furthermore, if the gas quantity becomes too large over time, under some circumstances the liquid flow velocity through the remaining un-blocked area of the screen can become so great that gas can also be pushed through the screen.